This project proposes to combine resources with a related project (R18 MH- 51391S; "HIV and Dual Diagnosed Homeless Individuals"; PI- Gary A. Morse, Ph.D.) to investigate HIV risk behaviors among seriously mentally ill persons who are homeless. Data from the additional one hundred and fifty participants in this study will be combined with baseline data from the dual diagnosis study, creating a larger data set for analysis. The result would be an analysis of HIV risk behaviors and its determinants for approximately 300 homeless persons with a serious mental illness, about half of whom would also have a substance abuse disorder. Social Cognitive Theory (Bandura, 1994) will be used as the theoretical framework for predicting HIV risk behaviors. Domains to be assessed include: knowledge of HIV transmission routes, sexual negotiation skills, self-efficacy for performing HIV prevention behaviors, and social support for HIV risk reduction. This study also proposes to investigate the characteristics of the participants' sexual partners, including where they met and if their sexual partners also had a serious mental illness or a substance abuse disorder. The results of this study could therefore have important consequences for HIV risk reduction programs focusing on SM! adults who are homeless.